Actually, something like it happened just after 9/11, when they stopped issuing the 30 year for a while, which had the effect of lowering rates further down the curve, of course.
QE1 couldn't support the dollar in the context of buying by China to keep the yuan down. QE2 just might, since the Chinese are now in tightening mode. Gold has been a bit equivocal since the Chinese began tightening, but still pointing up. If gold enters a mini-bear in the face of a QE2 announcement, we'll know the dollar will be supported.